There are many situations where it is desired to create a light field that has a specified luminance profile. Light projection systems have a very wide range of applications from architectural lighting to the display of lifelike images. The projected light patterns can be dynamic (e.g. video), static (used for static images or static applications like the beams of typical car headlights projected through a lens onto the road, made by arbitrarily shaped optical surfaces, etc.). Light may be projected onto a wide range of screens and other surfaces which may be flat or curved. Such surfaces may be fully reflective (like a canvas used in a cinema, a wall or a building) or partially reflective (such as the windshield of a vehicle). Screens may be low-gain or high-gain, Lambertian or highly directional, high-contrast or lower in contrast. Light may be projected onto solid objects or onto a medium in a volume (such as fog).
Markets for and applications of light projectors include digital cinema, in-door and out-door advertising, medical imaging (both for display of images, as well as capture by a smart light source), large venue and live events or performances, automotive heads up displays, car head-lights and rear-lights, automotive entertainment and information displays, home-theatre, portable business projection, television and displays for consumer applications, military applications, aviation applications (like cockpit displays, smart landing-assistance, individual passenger entertainment displays), structured light sources for industrial applications, automotive headlights and other applications. Structured light may also be used for high precision applications, such as curing ink or other material for 2D or 3D printing, or steering light for laser micro-machining.
Various devices may be used to spatially modulate light. These may be called spatial light modulators (SLMs). Most SLMs provide a 2D array of independently and individually addressable pixels. Some examples of SLMs are reflective SLMs such as digital micro-mirror devices (DMDs), liquid crystal on silicon (LCoS) devices and transmissive SLMs such as LCD panels, transmissive LCD chips such as high-temperature polysilicon (HTPS) or low-temperature polysilicon (LTPS); and partially reflective/partially transmissive SLMs such as micro-electro-mechanical systems (MEMS) based systems in which some of incident light is transmitted and some of incident light is reflected. Most readily available spatial light modulation technologies are subtractive. These SLM technologies operate by absorbing or removing undesired light.
Other types of devices may controllably alter the nature and/or distribution of light using techniques that are not primarily subtractive. For example, the light redistributor may exploit interference of electro-magnetic waves (light), to modulate the distribution of light by controlling its phase characteristics and/or modulate the frequency of the light in order to change the apparent colour of light. Both of these examples show how light can be changed without converting energy from the light into wasted heat by absorbing the light.
Examples of dynamically-addressable focusing elements include: transmissive 2D arrays of controllable liquid crystal compartments with the property that the compartments can be controlled to selectively retard the phase of light, effectively causing a change in path-length. Devices that can controllably adjust the phase of light of different areas are called Phase Modulating Devices (PMD). PMDs may be transmissive or reflective. Some PMDs can individually control phase in a 2D array made up of a large number of pixels. A dynamically-addressable focusing element may also affect the polarization of light. Some devices may alter several light properties simultaneously.
Other types of dynamically-addressable focusing element comprise one or more scanning mirrors, such as a 2D or 3D microelectromechanical system (MEMS); and/or one or more deformable lenses or mirrors or other optical elements. A dynamically-addressable focusing element may also or in the alternative comprise one or more optical switches.
Various sources can be used for illuminating SLMs, PMDs, imaging chips, or any other light re-distributing device, including arc lamps, light-emitting diodes (LEDs), LEDs plus phosphor, lasers, lasers plus phosphors. Each light source may emit light of different shapes, intensities and profiles. Traditional approaches to combining multiple light sources into a single higher-powered source include coupling light into optical fibres, and knife edge mirror beam combining, relaying into an integration rod, or some other optical averaging device.
However, in some cases, the useful characteristics of individual low-powered light sources are not preserved when combined using the traditional approaches, and higher-powered single-emitters are either not available, or have a prohibitively high cost per watt of light. For example, when light from multiple laser diodes is combined some of the characteristics affected are:                Coherence: When coupling light from multiple discrete laser diodes or laser diode bars into a multi-mode fibre, or combining multiple laser beams into a single beam using a knife edge mirror array plus lens, coherence is lost.        Polarization: The light at the output of a multi-mode fibre is no longer polarized, so some polarization recovery techniques must be used for applications that require polarized light.There is a need for light sources and projectors that effectively combine light from multiple light sources. There is a particular need for cost-effective light sources and projectors in which light from multiple light sources can be manipulated to yield desired light patterns having desired optical characteristics.        